1. Field of the Invention.
The present invention relates generally to electrostatic paint spraying equipment, and more particularly to an apparatus which fits over the feed tube and the barrel of a standard electrostatic spray gun and acts both to protect the hand of the spray gun operator from an electrostatic discharge and to channel the discharge to an indicator light installed in a prominent place, illuminating the indicator light and providing an indication of operation of the electrostatic spray gun.
2. Description of the Related Art.
Electrostatic spray guns provide particular advantage in a spray painting operation in which a conductive article is to be painted. The article to be painted is grounded, and a strong electrostatic field is developed between paint emanating from the spray gun and the article. The electrostatic field is typically created by installing an electrode on or near the spray gun, with the electrode desirably being located in the vicinity of the atomization orifice in the nozzle of the spray gun.
The typical electrode has a tip which forms an abrupt discontinuity such as a sharp needle or a keen edge. Such a sharp discontinuity will enable the formation of the highest electrostatic field intensity in the environs of the discontinuity. By placing the tip of the electrode having the sharp discontinuity in the vicinity of the atomization orifice in the nozzle of the spray gun, the atomized paint particles will thus be subjected to this maximum electrostatic field intensity. This effectively operates to charge the atomized paint particles with respect to the article being painted.
The spray gun operates to generate a fine mist of atomized paint particles emanating from the atomization orifice in the nozzle of the spray gun. Typically, atomization may be accomplished through impinging jets of high velocity air acting on an emitted column of paint, or by very high hydraulic pressure forcing the paint through a highly restricted atomization orifice. In either event, the finely atomized paint particles are sprayed from the atomization orifice in close proximity to the tip of the electrode having the sharp discontinuity to charge the atomized paint particles.
The fact that the finely atomized paint particles are highly charged with respect to the article being painted provides an attractive force between the paint particles and the article. This results in two advantages, the first of which is that since the paint is attracted to the article being painted, there will be less overspray and less wasted paint. The other advantage is that the paint particles will form a highly uniform coating on the article being painted, thus resulting in a high quality finished appearance which is highly desirable.
It will of course be realized by those skilled in the art that the electrostatic field represents a very high voltage potential. The electrostatic field affects portions of the spray gun at times by causing voltage to build up on portions of the spray gun such as the paint supply tube between the nozzle of the spray gun and the base of the handle of the spray gun, or on the barrel of the spray gun. When sufficient voltage builds up on one of these portions of the spray gun, a discharge may arc from the charged portion of the spray gun to the operator's hand. To say the least, this is an unpleasant experience which is highly undesirable, and which may well be hazardous.
It is accordingly the primary objective of the present invention that it protect the operator from discharge arcs occurring as a result of voltage buildup on portions of the spray gun. It is of course desirable that the operation of the present invention represent a complete protection of the operator to the greatest extent possible. As such it is a further objective that the operation of the present invention act to prevent charge from building up on the portions of the spray gun over a period of time to an extremely high potential.
One of the other problems encountered in the field of electrostatic spray painting is that it is desirable to provide an indication that the electrostatic operation is functioning properly. It will be realized by those skilled in the art that the electrostatic field generated is invisible, and that only a highly experienced operator can detect when the electrostatic field is not being generated. In the past various voltage indicators have been incorporated into the design of power supplies. Unfortunately, the problem usually occurs separately from the power supply, in the spray gun itself.
There has been one significant attempt to solve this problem, which is shown in U.S. Pat. No. 4,682,735, to Mommsen. The Mommsen invention incorporates an indicator light into the spray gun itself, with one side of the indicator light being grounded and the other side being placed in proximity to the electrostatic field being generated by the spray gun. When the light is illuminated, it is thus ascertained that the electrostatic operation of the spray gun is working properly.
In actual operation, the Mommsen light may not be highly visible to the operator, and thus may not be easily observed. In addition, many users of electrostatic paint guns will employ a protective cover on the spray gun to protect it from overspray. Such a cover will be placed over the Mommsen light, thus effectively preventing it from providing its highly useful signal to the operator. Finally, it will be realized that the signal provided by the Mommsen design that the electrostatic operation of the spray gun is functioning properly is visible only to the operator in the spray booth.
It is thus an additional objective of the present invention that it provide a more visible signal that the electrostatic operation is in fact functioning properly. The signal should be located away from the spray gun so that a protective cover placed over a portion of the spray gun will not obstruct the signal. In addition, the signal should be visible not only to the operator of the spray gun, but it should be visible to others without entering the spray painting booth.
Both the protection accorded to the operator from electrical discharge and the more visible signal of proper electrostatic operation should be accomplished in as expeditious a manner as possible. The improvements of the present invention should be obtained at as low a cost as possible, thereby making the solution of the present invention highly desirable from an economic standpoint. Finally, it is also an objective of the present invention that all of the aforesaid advantages and objectives be achieved without incurring any substantial relative disadvantage.